The present invention relates to a container for storing food and liquids with a removable and replaceable lid capable of producing a tight seal. The container of the present invention is particularly directed for use in microwave cooking in which the container should be fairly strong so that it can hold a reasonable quantity of material and be placed into a microwave oven where it is subjected to RF energy from a source such as a magnetron.
The containers normally are plastic material, for example, polypropylene or polyethylene polymers and copolymers, and are fairly rigid although they may be subject to some amount of flexure. The lid provided must be capable of properly and effectively sealing the container to keep out ambient air. The lid must also be relatively easy to remove and replace since the container and lid are normally to be re-used.
A variety of container lid constructions are available, each of which has been designed to achieve the aforesaid goals or for a specific purpose or purposes. Most container lid combinations provide a sealing bead or rim around the container wall peripheral upper edge and a mating channel on the lid. The two fit together to produce the seal. Some lids are designed to be relatively elastic and flexible with a slow rate of recovery to provide a non-snapping and noiseless type of action when the lid is supplied to the container. Because of the use of plastic material having high flexibility to obtain a non-snapping lid, its difficult with such a construction to provide a tight seal especially under conditions where the container is refrigerated. Moreover, if the lid has a recessed top wall, this reduces the capacity of the container for storing foods. Such an arrangement is shown in U.S. Pat. No. 2,487,400.
Another type of container lid, such as shown in U.S. Pat. No. 4,471,880 to Tagle, uses a snap action by providing a cantilever type construction between the medial lid portion and the sealing channel on its periphery combined with a special shape for the container sealing bead. However, such an arrangement may not provide an effective seal after extended use due to the dimensional changes between the bead and the sealing channel.
One desirable material to use for such container is a polypropylene copolymer which can be produced in a clear transparent version. This material is desirable since it is relatively rigid and, being transparent, it permits the user to view the contents of the container during the time that it is in the microwave oven. It would be also desirable to use this material for the lid since it would provide better structural rigidity for the container lid combination and also permit a clear view of the container contends through the lid. However, such a material has a problem in that it is relatively stiff and inflexible. Thus, some effective way must be found to provide an effective seal using a relatively stiff and rigid material for the lid. This is why, in many prior art containers/lid combinations, the lid is often made of more flexible material than the container.